1. Field of the Invention
This invention relates to the preparation of sodium bicarbonate from sodium carbonate, sodium sesquicarbonate, and/or Wegscheider's salt, by effecting a reversion of the solid feed, in an aqueous medium, to crystalline sodium bicarbonate.
2. Description of the Prior Art
Sodium bicarbonate (NaHCO.sub.3) is conventionally prepared by carbonation of aqueous sodium carbonate (Na.sub.2 CO.sub.3); see R.N. Shreve et al, Chemical Process Industries, McGraw-Hill Book Co., 4th ed., 1977, p. 213.
Commercial bicarbonate processes first dissolve soda ash in an aqueous liquor and then introduce the saturated sodium carbonate solution into a carbonating tower or vessel, where it is intimately contacted with carbon dioxide gas and simultaneously cooled.
The crystallized sodium bicarbonate is withdrawn from the carbonating tower as an aqueous slurry, filtered, and dried. The aqueous liquor that remains after filtration of the solid sodium bicarbonate is used to dissolve more soda ash to continue the cyclic carbonation process.
This carbonation process, as well as other prior art carbonation procedures, suffers from several operating drawbacks: scale-formation on equipment surfaces; parallel equipment lines required to allow for periodic clean-outs; significant energy and corrosion costs due to hot operating temperatures; low product slurry density per pass due to limited sodium carbonate solubility.
Other carbonation processes for the production of sodium carbonate have also been disclosed in the prior art; in these an alkali other than aqueous sodium carbonate solution is treated with carbon dioxide.
European Patent Application Publication No. 5,981 (assigned to Stauffer Chemical Co.) describes the carbonation of a saturated solution of sodium carbonate and sodium bicarbonate or, alternatively, a slurry of sodium bicarbonate in such saturated solution, or a slurry of sodium bicarbonate and sodium sesquicarbonate in such saturated solution. A satisfactory crystalline sodium bicarbonate product is ensured by the presence of specific amounts of Ca.sup.++ ion in solution during the carbonation.
U.S. Pat. No. 3,780,160, issued to Waggener et al on Dec. 18, 1973, describes the multistep manufacture of sodium bicarbonate from trona (crude sodium sesquicarbonate). Trona ore is dissolved in aqueous liquor, and sodium sesquicarbonate is crystallized by vacuum cooling of the aqueous sodium bicarbonate-sodium carbonate solution. The crystalline sodium sesquicarbonate is recovered, and redissolved in a second aqueous liquor. This second aqueous sodium bicarbonate-sodium carbonate solution is then carbonated to produce crystalline sodium bicarbonate, which is recovered and dried.
U.S. Pat. No. 2,704,239, issued to Pike on Mar. 15, 1955, describes the production of a sodium bicarbonate intermediate from trona ore and next calcining the crystalline sodium bicarbonate to yield a light density soda ash. The bicarbonate intermediate is obtained by first dissolving trona ore in an aqueous, hot liquor containing sodium bicarbonate and sodium carbonate, treating such solution with carbon dioxide to increase its bicarbonate content and then cooling or concentrating such solution to crystallize sodium bicarbonate. The crystalline sodium bicarbonate may be recovered and dried or, alternatively, calcined to form a light soda ash.
The method of this invention yields a sodium bicarbonate product with good crystal habit and sizing, without resorting to the conventional direct carbonation, cooling crystallization processes of the prior art.